Highly stable Ni—M F6—NH2O/onpyrazine2(solvent)x metal organic frameworks and methods of use

ABSTRACT

Provided herein are metal organic frameworks comprising metal nodes and N-donor organic ligands. Methods for capturing chemical species from fluid compositions comprise contacting a metal organic framework characterized by the formula [M a M b F 6-n (O/H 2 O) w (Ligand) x (solvent) y ] z  with a fluid composition and capturing one or more chemical species from the fluid composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/564,920, filed Oct. 6, 2017, which is a U.S. National StageApplication of Application No. PCT/IB2016/05199, filed Apr. 7, 2016,which claims priority to U.S. Provisional Application No. 62/144,169,filed Apr. 7, 2015, which application is incorporated herein byreference.

BACKGROUND

Within many industries today, removal of volatile organic compounds(VOCs) from gases is a worldwide priority due to their health risks andharmful effects on the environment. In particular, organizations such asthe Environmental Protection Agency have placed strict limits on theemission of certain classes of VOCs, including BTX (benzene, toluene,xylene), BTEX (benzene, toluene, ethylbenzene, and xylene), BTEXN(benzene, toluene, ethylbenzene, xylene, and naphthalene), and TEXS(benzene, toluene, ethylbenzene, xylene, and styrene). However,separation and capture of such VOCs remain some of the most intensiveand challenging industrial separations. Further, the presence of VOCs ingasses frustrates many industrial processes. For example, aminescrubbing is a common process used to remove acid gases such as CO₂ andH₂S from raw gas, but the amine process solution is easily contaminatedby VOCs such as BTX and BTEX present within the gas.

Solid, porous material systems are a developing class of materials thathave potential to solve or alleviate many technical problems generallygermane to gas capture. Zeolite materials have long been used in manygas capture applications, but suffer from limited gas selectivity andcyclic adsorption performance in the presence of moisture. Metal organicframeworks (MOFs) are a new class of material which generally includeporous crystals assembled from modular molecular building blocks, andprovide a wide array of advantageous material properties including highsurface area, porosity, and sorption potential. While the availablebuilding block options, and combinations thereof, are virtuallylimitless, such potential highlights the statistical difficulty inidentifying and assembling MOFs with desired and particularized materialproperties and multi-faceted functionality. For example, many MOFsexhibit high selectivity towards a particular molecular species, but arehighly intolerant to water.

SUMMARY

In general, this disclosure describes porous metal organic frameworks(MOFs). In particular, this disclosure describes MOFs suitable for thecapture and removal of gases and/or vapors from fluids. It should benoted that although the embodiments of this disclosure are describedwith respect to examples for gas capture, the embodiments describedherein are generally applicable to many fields including gas moleculeseparation, gas storage, catalysis, sensors, drug delivery, rare gasseparation, and proton conductivity.

As provided herein, a method of capturing chemical species from a fluidcomposition can comprise contacting a metal organic frameworkcharacterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) with a fluidcomposition comprising two or more chemical species and capturing one ormore captured chemical species from the fluid composition.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments ofthe invention.

FIGS. 1A-B illustrate schematic views of a metal organic framework,according to one or more embodiments of this disclosure.

FIG. 2 illustrates a method for fabricating a metal organic framework,according to one or more embodiments of the disclosure.

FIG. 3 illustrates a method for capturing chemical species from fluidcompositions, according to one or more embodiments of the disclosure.

FIGS. 4A-B illustrate powder X-ray diffraction data of metal organicframeworks, according to one or more embodiments of this disclosure.

FIG. 5A illustrates propane sorption isotherm data of a metal organicframework, according to one or more embodiments of this disclosure.

FIG. 5B illustrates a method for utilizing a metal organic framework asa molecular sieve, according to one or more embodiments of thisdisclosure.

FIGS. 6A-B illustrate hydrocarbon sieving data, according to one or moreembodiments of this disclosure.

FIG. 7A illustrates benzene sorption isotherm data of a metal organicframework, according to one or more embodiments of this disclosure.

FIGS. 8A-C illustrate H₂O sorption isotherm data of various metalorganic frameworks, according to one or more embodiments of thisdisclosure.

FIG. 8D illustrates a comparison of the relationship between wateruptake at 0.05 P/P₀, heat of sorption and regeneration temperature ofvarious metal organic frameworks, according to one or more embodimentsof this disclosure.

FIGS. 9A-C illustrate CO₂ sorption isotherm data of various metalorganic frameworks, according to one or more embodiments of thisdisclosure.

FIGS. 9D-E illustrate CO₂ guest molecules inside a metal organicframework, according to one or more embodiments of this disclosure.

FIG. 9F illustrates CO₂ heat of sorptions of a metal organic framework,according to one or more embodiments of this disclosure.

FIG. 9G illustrates cyclic CO₂/N₂ column breakthrough experiments for anMOF, according to one or more embodiments of this disclosure.

FIG. 9H illustrates a heat of adsorption-CO₂ uptake trade-off for ametal organic framework as compared to benchmark and new developedmaterials, according to one or more embodiments of this disclosure.

DETAILED DESCRIPTION

Provided herein are a series of highly stable and highly tunable MOFswith high affinity and stability to water and H₂S. Such qualities allowfor efficient and cost effective methods for dehydrating gases, vapors,and solvents capable of replacing many cumbersome and expensiveindustrial processes. Further, this novel series of MOFs can be designedwith a variety of pore sizes and assembled with and without open-metalsites, affording tunable properties for a variety of separationapplications. For example, the MOFs provided herein can refinehydrocarbon fluids under conditions and in the presence of chemicalspecies which render known technologies inefficient, impracticable, orinoperable. In particular, MOFs provided herein can perform molecularsieving of fluid mixtures such as olefin/paraffin mixtures. In anotherexample, the MOFs described herein are suitable for applicationsinvolving BTX removal from fluid compositions comprising H₂S, whichoffers enormous cost savings by protecting and maintaining the operationefficiency of Claus catalysts.

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the invention.Several aspects of the invention are described below with reference toexample applications for illustration. It should be understood thatnumerous specific details, relationships, and methods are set forth toprovide an understanding of the invention. One skilled in the relevantart, however, will readily recognize that the invention can be practicedwithout one or more of the specific details or with other methods. Inother instances, well-known structures or operations are not shown indetail to avoid obscuring the invention. The present invention is notlimited by the illustrated ordering of acts or events, as some acts mayoccur in different orders and/or concurrently with other acts or events.Furthermore, not all illustrated acts or events are required toimplement a methodology in accordance with the present invention.

As used herein, “fluids” can refer to a gas, liquid, or combinationthereof. A gas or liquid can include one or more components. Forexample, a fluid can include a gas stream comprising CO₂, H₂S and watervapor.

As used herein, “refining” refers to removing one or more unwantedcomponents or separating one or more components from remainingcomponents of a composition. For example, refining can include removingolefin chemical species from a fluid composition, such as a mixture ofolefin and paraffin chemical species.

As used herein, “poly-functional” refers to the characteristic of havingmore than one reactive or binding sites. For example, a poly-functionalligand can attach to a metal ion in multiple ways, bridge multiple metalions, or combinations thereof. Specifically, pyrazine is apoly-functional ligand.

As used herein, “olefin” refers to an unsaturated hydrocarbon moleculeincluding a carbon-carbon double bond. Olefins are also referred to asalkenes. An example of an olefin is propene.

As used herein, “paraffin” refers to a saturated hydrocarbon moleculeconsisting of carbon and hydrogen atoms connected only by single bonds.Paraffins are also referred to as alkanes. An example of a paraffin ispropane.

Gas storage and separation using porous materials has experiencedsignificant development in recent years in various industrialapplications related to energy, environment, and medicine. Among porousmaterials, metal organic frameworks (MOFs) are a versatile and promisingclass of crystalline solid state materials which allow porosity andfunctionality to be tailored towards various applications. MOF crystalchemistry uses a molecular building block (MBB) approach that offerspotential to construct MOFs where desired structural and geometricalinformation are incorporated into the building blocks prior to theassembly process.

Generally, MOFs comprise a network of nodes and ligands, wherein a nodehas a connectivity capability at three or more functional sites, and aligand has a connectivity capability at two functional sites each ofwhich connect to a node. Nodes are typically metal ions or metalcontaining clusters, and, in some instances, ligands with nodeconnectivity capability at three or more functional sites can also becharacterized as nodes. In some instances, ligands can include twofunctional sites capable of each connecting to a node, and one or moreadditional functional sites which do not connect to nodes within aparticular framework. A MBB can comprise a metal-based node and anorganic ligand which extrapolate to form a coordination network. Suchcoordination networks have advantageous crystalline and porouscharacteristics affecting structural integrity and interaction withforeign species (e.g., gases). The particular combination of nodes andligands within a framework will dictate the framework topology andfunctionality. While essentially limitless combinations of nodes andligands exist, to date, very few MOF materials are H₂S stable whichconsequently preclude their use in gas separation.

As disclosed in co-owned U.S. Application No. 62/044,928, a series ofisoreticular MOFs with periodically arrayed hexafluorosilicate (SiF₆)pillars, called SIFSIX-2-Cu-i and SIFSIX-3-Zn, SIFSIX-3-Cu andSIFSIX-3-Ni showed particularly high CO₂ selectivity and capture. Theseproperties in SIFSIX-3-M materials suggest broad applications from ppmlevel CO₂ removal to bulk CO₂ separation. However, with the exception ofSIFSIX-3-Ni, the SIFSIX-3-M materials were not tolerant to H₂S. Andalthough these materials exhibit high structural structurally in thepresence of CO₂, extensive exposure of all SIFSIX-3-M materials tomoisture detrimentally induces a phase change and the formation of new2D stable materials. These 2D materials exhibit relatively unalteredselectivity but diminished CO₂ uptake. This indicates that theSIFSIX-3-M materials series is not sufficiently robust to handle CO₂ andH₂S capture in most critical applications throughout the oil and gas andrenewable fuels industries, especially in applications which bring thematerials into contact with moisture.

MOFs, as provided herein, comprise one or more MBBs. Generally, a MBB,or a network of MBBs, can be represented by the formula[(node)_(a)(ligand)_(b)(solvent)_(c)]_(n), n represents the number ofmolecular building blocks. Solvent represents a guest molecule occupyingpores within the MOF, for example as a result of MOF synthesis, and canbe evacuated after synthesis to provide a MOF with unoccupied pores. Inone example, an evacuated MOF can be subsequently enriched with a guestmolecule compatible with the MOF framework and/or pores for a particularpurpose (e.g., to outfit the MOF for use as a sensor). In otherembodiments, guest molecules can include adsorbed gases, such as H₂S.While guest molecules can impart functionality onto a MOF, such are nota permanent fixture of the MOF. Accordingly, the value of c can varydown to zero, without changing the definitional framework of the MOF.Therefore in many instances, MOFs as provided herein will be defined as[(node)_(a)(ligand)_(b)]_(n), without reference to a solvent or guestmolecule component.

In some embodiments herein, MOFs can be characterized by the formula[(node)_(a)(ligand)_(b)(solvent)_(c)]_(n). A non-limiting list ofsolvents can include one or more of H₂O, DMF, and DEF. In someembodiments, solvent can include a chemical species present afterfabrication of the MOF. Some embodiments herein comprise a porous,uninhabited MOF characterized by the formula[(node)_(a)(ligand)_(b)]_(n), wherein node comprises, generally,M_(a)M_(b)F_(x)O_(y)(H₂O)_(z). In some embodiments, M_(a) compriseselements selected from periodic groups IB, IIA, IIB, IIIA, IVA, IVB,VIB, VIIB, or VIII. In some embodiments, M_(b) comprises elementsselected from periodic groups IIIA, IIIB, IVB, VB, VIB, or VIII. In someembodiments, M_(a) comprises elements selected from periodic groups IB,IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, or VIII and M_(b) compriseselements selected from periodic groups IIIA, IIIB, IVB, VB, VIB, orVIII. In some embodiments, M_(a) can comprise one of the followingcations: Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺,Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺,Ru³⁺ and Co³. In some embodiments, M_(b) can be one of the followingAl⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺. Insome embodiments, M_(a) can comprise one of the following cations: Cu²⁺,Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺,Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺ and Co³;M_(b) can be one of the following Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺,V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺. In such embodiments, the ligand can beany bi-functional N-donor linkers based on monocyclic or polycyclicgroup (aromatic or not).

In some embodiments, a ligand can comprise a polydentate, orpoly-functional ligand, such as a bi-functional ligand, a tri-functionalligand, or ligands with four or more functional sites. In someembodiments, a ligand can comprise an N-donor linker. In someembodiments a ligand can comprise a poly-functional ligand. In someembodiments, a ligand can comprise a plurality of N-donor functionalgroups. In some embodiments, a ligand can comprise a monocyclic orpolycyclic group structure, wherein the cyclic groups can be aromatic ornon-aromatic. In some embodiments, a ligand can comprise anitrogen-containing monocyclic or polycyclic group structure. In someembodiments, a ligand can comprise a nitrogen-containing heterocyclicligand, including pyridine, pyrazine, pyrimidine, pyridazine, triazine,thiazole, oxazole, pyrrole, imidazole, pyrazole, triazole, oxadiazole,thiadiazole, quinoline, benzoxazole, benzimidazole, and tautomersthereof.

Some embodiments of suitable MOFs can be represented by the followinggeneral formula: [M_(a)M_(b)F_(x)(O/H₂O)_(z)(Ligand)₂]_(n) wherein M_(a)can be one of the following cations: Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺,Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺²,Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺ and Co³; M_(b) can be one of the followingAl⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺; andthe ligand can be any bi-functional N-donor linkers based on monocyclicor polycyclic group (aromatic or not).

One MOF synthesis strategy provided herein comprises linking inorganicchains using appropriate N-donor based linkers to deliberately generatechannels along one crystallographic direction. The inorganic chains arebuilt up from the trans-connection between M_(a)N₄F₂ and M_(b)F₄(H₂O)₂octahedra or between M_(a)N₄F₂ and M_(b)F₅(H₂O) octahedra or betweenM_(a)N₄F₂ octahedra and M_(b)F₅(O) octahedra. FIG. 1A illustrates anexample of an inorganic chain, built up from M_(a)N₄F₂ and M_(b)F₅(H₂O)octahedra. The resulted inorganic chains are linked to each other usingbi-functional N-donor organic ligands, thereby generating channels withdifferent sizes and shapes depending on the nature of the organiclinker. FIG. 1B illustrates a schematic view of one embodiment of a MOFcomprising a NiNbF₅O(pyrazine)₂ structure, viewed along the c-axis.

The utility of MOFs such as those provided herein are highly dependentupon the framework's structural features such as structural strength,density, functionality, pore aperture dimensions, pore dimensions, theratio of pore aperture dimensions to pore dimensions, poreaccessibility, and the presence of a plurality of pore dimensions and/orpore aperture dimensions (e.g., a poly-porous MOF). The originality ofthis new class of crystalline porous materials is based, in part, on thefact that the shape of cavities, (i.e. square or rectangle basedchannels), is controlled from a structural point of view usingappropriate cations and organic linkers. The novel MOF architecturesdisclosed herein offer a novel improvement on some MOF architectures byreplacing silicon components with other metals, such as Al³⁺, Fe²⁺,Fe³⁺, V³⁺, V⁴⁺, V⁵⁺, Nb⁵⁺, to afford highly stable materials with orwithout open metals sites. In some embodiments, the use of specificcations, such as Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺,In³⁺, Y³⁺, in M_(b) site positions can introduce open-metal sites withinthe channels that enhance properties of gas capture.

These, and other features, collaborate to achieve MOFs with highaffinity and stability to water and H₂S. Additionally, the novel seriesof MOFs structures disclosed herein can be designed with a variety ofpore sizes and/or open-metal sites which afford tunable properties for avariety of gas/vapor/solvent separation applications. Tuning, in someembodiments, can include modification of the organic and/or inorganiccomponents of the MOF. For example, lighter metal-based clusters can beused to lower the framework density and increase the relative wt. % ofcaptured CO₂ and/or H₂S. Further, the MOF platforms as provided hereinallow for an unprecedented high degree of tuning control at themolecular level, allowing the size and shape of channels within a MOFarchitecture to be rigorously controlled and adapted to specificseparation of numerous gases, beyond CO₂ and H₂S.

In some embodiments, a representative[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFstructure can include a Ni M_(a) constituent, an M_(b) constituent groupselected from one of Al, Fe, V, or Nb, and a Ligand comprising apyrazine constituent group. All such embodiments offer high affinity andstability to water vapor and H₂S, unlike the Cu and Zn-based analoguesof SIFSIX-3-M materials made with Si. In in some embodiments a MOFcharacterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) whereinM_(a) equals Ni, M_(b) equals Al, Fe, V or Nb, and ligand equalspyrazine, the pore size (channel size) of the resulting MOF can be about3.3 Å to about 3.8 Å, or about 2.8 Å to about 4.8 Å. In someembodiments, the channels are square/rectangular. In the same or in analternative embodiment, a MOF can have a specific surface area of about250 m2/g to about 500 m2/g. In either of the same MOFs or in analternative embodiment, a MOF can have a pore volume of about 0.1 cm3/gto about 0.25 cm3/g. In a different embodiment, a more elongated ligandcan provide an analogous MOF with much higher porosity.

In some embodiments, M_(b) and/or a ligand can be selected to hinder orallow rotation of a ligand. Altering the nature, shape, and dimensionsof the (M_(b)OF₅)^(x−) pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of ligands and thus dictate themaximum and/or minimum opening of the pore aperture size. This approachoffers potential to dial-in/command the passing-blocking of specificprobe molecules. In some embodiments M_(b) and/or a ligand are selectedto allow no rotation of a ligand. In some embodiments M_(b) and/or aligand are selected to allow full rotation of a ligand. In someembodiments M_(b) and/or a ligand are selected to allow partial rotationof a ligand.

In some embodiments, M_(b) and/or a ligand can be selected to hinder orallow rotation of a pillar. Altering the nature, shape, and dimensionsof the (M_(b)OF₅)^(x−) pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of pillars and thus dictate themaximum and/or minimum opening of the pore aperture size. This approachoffers potential to dial-in/command the passing-blocking of specificprobe molecules. In some embodiments M_(b) and/or a ligand are selectedto allow no rotation of a pillar. In some embodiments M_(b) and/or aligand are selected to allow full rotation of a pillar. In someembodiments M_(b) and/or a ligand are selected to allow partial rotationof a pillar.

In some embodiments, M_(b) and/or a ligand can be selected to hinder orallow rotation of a ligand and a pillar. Altering the nature, shape, anddimensions of the (M_(b)OF₅)^(x−) pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of a ligand and a pillar and thusdictate the maximum and/or minimum opening of the pore aperture size.This approach offers potential to dial-in/command the passing-blockingof specific probe molecules. In some embodiments M_(b) and/or a ligandare selected to allow no rotation of a ligand and a pillar. In someembodiments M_(b) and/or a ligand are selected to allow full rotation ofa ligand and a pillar. In some embodiments M_(b) and/or a ligand areselected to allow partial rotation of a ligand and a pillar.

A specific MOF characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) isNbOFFIVE-1-Ni, wherein M_(a) comprises Ni and M_(b) comprises Nb. ThisMOF includes a (NbOF₅)²⁻ inorganic pillar which, due to the larger Nb⁺⁵,has a longer Nb—F bond length (1.905(1) Å) as compared to the Si—F bondlength (1.681(1) Å) of the SIFSIX MOFs described above. The increasedNb—F bond length reduces the distance between the pendant fluorine inthe channel, and the relatively increased nucleophile behavior of(NbOF₅)²⁻ provides increased stability in the presence of water.Pyrazine is a suitable ligand for the NbOFFIVE-1-Ni MOF, among others asdescribed herein. NbOFFIVE-1-Ni is a pillared sql-MOF based on (NbOF₅)²⁻pillars that connect a 2D square grid of Ni-(pyrazine)₂. Thequadrangular-pillared sql-MOF can be viewed as a 3D MOF wherein eachNiOF(pyrazine)₄ node serves as 6-connected node connected by (NbOF₅)²⁻pillars through fluorine/oxygen atoms giving rise to a pcu topology. Itmust be noted that the assignment of one oxygen and one fluorine atom inapical position within the pillar has been previously demonstrated insimilar materials and confirmed with supporting techniques.¹² Theoverall framework consists of square shaped open channels havingslightly smaller diameters of about 3.175(1) Å (taking account of vander Walls radii) comparatively to the analogue material SIFSIX-3-Cu(3.980(1) Å).

A specific MOF characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) isAlFFIVEH₂O-1-Ni, wherein M_(a) comprises Ni and M_(b) comprises Al. Whenutilizing a pyrazine ligand, this MOF can be characterized by thespecific formula NiAlF₅(H₂O)(pyr)₂.2H₂O, although other ligandsdescribed herein can be suitable. Another specific MOF characterized bythe formula [M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z)is FeFFIVEH₂O-1-Ni, wherein M_(a) comprises Ni and M_(b) comprises Fe.When utilizing a pyrazine ligand, this MOF can be characterized by thespecific formula NiFeF₅(H₂O)(pyr)₂.4H₂O, although other ligandsdescribed herein can be suitable. AlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Niare isomorphs, and take advantage of the periodically arrayed fluorinecombined with the adequate one dimensional channel size. In contrast tothe Si of SIFSIX MOFs described above, the introduction of open metalsites within the framework is concomitant with the utilization of anappropriate metal with the required oxidation state that allows thepresence of a water molecule within the metal coordination sphere.Aluminum and Iron cations were used such that the MOF would adopt anoctahedral fluorinated environment and lead to open metal sites aftercoordinated water removal via proper activation. Each isomorph utilizingpyrazine as a ligand exhibits a primitive cubic (pcu) topology resultingfrom the pillaring of metal-pyrazine 2D square-grid moieties with(MF₅H₂O)²⁻ (M=Al³⁺ or Fe³⁺) inorganic pillars.

Some such MOFs can be fabricated using a solvo(hydro)thermal syntheticprocedure. As shown in FIG. 2, a method for fabricating 200 a MOF 230can include combining 205 reactants. Reactants can include one or moreof a fluorhydric acid solution 206 with a Ni²⁺ source 207, a secondmetal source 208, and a solvent 209 to form a mixture 210. A Ni²⁺ source207 can include one or more of nickel nitrate, hydrated nickel nitrate,nickel chloride, hydrated nickel chloride, nickel fluoride, hydratednickel fluoride, nickel oxide, or hydrated nickel oxide. The secondmetal source 208 can include an Al⁺³ source, an Fe⁺² source, an Fe⁺³source, a Cr²⁺ source, a Cr³⁺ source, a Ti³⁺ source, a V³⁺ source, a V⁵⁺source, a Sc³⁺ source, an In³⁺ source, a Nb⁵⁺ source, or a Y³⁺ source,for example. These, metals can be in the form of nitrates, hydratednitrates, chlorides, hydrated chlorides, fluorides, hydrated fluorides,oxides, hydrated oxides, and combinations thereof. The solvent 209 caninclude one or more of H₂O, dimethylformamide (DMF), anddiethylformamide (DEF).

The method for fabricating 200 can further comprise to reacting 215 themixture 210, sufficient to form a reacted mixture 220. Reacting 215 caninclude contacting the fluorhydric acid solution 206, the Ni²⁺ source207, the second metal source 208, and the solvent 209. Reacting 215 canfurther comprise stirring or agitating the mixture 210, or heating themixture 210. Heating the mixture 210 can comprise heating to atemperature between about 80° C. to about 200° C. The reacted mixture220 can be further processed 225 to provide a fabricated MOF 230.Processing 220 can include one or more of filtering the reacted mixture220, rinsing the reacted mixture 220 with water, removing excessreactants from the reacted mixture 220. In some embodiments, guestmolecules are optionally evacuated from a fabricated MOF 230. Guestmolecules can include solvent guest molecules, or derivatives thereof.

FIG. 3 illustrates a method 300 for capturing 320 one or more chemicalspecies from a fluid composition 310 via a MOF 305. A method 300 forcapturing 320 one or more chemical species from a fluid composition 310can comprise contacting 315 a metal organic framework 305 characterizedby the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) with a fluidcomposition 310. Fluid composition 310 can comprise two or more chemicalspecies. Method 300 can further comprise capturing 320 one or morecaptured chemical species from the fluid composition 310. In someembodiments, capturing 320 comprises physical adsorption of the one ormore captured chemical species by the metal organic framework 305. Insome embodiments, capturing 320 comprises chemisorption of the one ormore captured chemical species by the metal organic framework.Chemisorption can occur by one or more captured chemical specieschemically interacting with one or more open metal sites of the metalorganic framework 305. In other embodiments, capturing 320 comprisesphysical adsorption and chemisorption of the one or more capturedchemical species by the metal organic framework. Capturing can comprisewholly or partially containing a chemical species within a pore of aMOF. In some embodiments, capturing 320 consists of chemisorption. Insome embodiments, capturing 320 consists of physical adsorption.

In some embodiments, the fluid composition 310 can comprise H₂S and oneor more of benzene, toluene, xylene, ethylbenzene, naphthalene andstyrene. In such embodiments, capturing 320 can comprise capturing oneor more of benzene, toluene, xylene, ethylbenzene, naphthalene, andstyrene. In a specific embodiment, M_(a) can comprise Ni2+ and M_(b) cancomprise Nb5+.

In some embodiments, the fluid composition 310 can comprise breathableair. Breathable air can include atmospheric air, or life-supporting airin a confined space. In a non-limiting example, breathable air caninclude one or more of oxygen, nitrogen, carbon dioxide, and argon. Insuch embodiments, capturing 320 can comprise capturing carbon dioxide.In such embodiments, capturing 320 can consist of capturing carbondioxide. In such embodiments, capturing 320 occurs in a confined space.Capturing 320 can comprise capturing trace amounts of carbon dioxide.

In some embodiments, the fluid composition 310 can comprise one or moreof flue gas, syngas, biogas and landfill gas. In such embodiments,capturing 320 can comprise capturing carbon dioxide. In suchembodiments, capturing 320 can consist of capturing carbon dioxide.

In some embodiments, the fluid composition 310 can comprise one or moregases, one or more vapors, one or more solvents, or combinationsthereof. In such embodiments, capturing 320 can comprise capturingwater. In such embodiments, capturing 320 can consist of capturingwater. In one embodiment, M_(a) can comprise Ni2+ and M_(b) can compriseFe+2 or Fe+3.

In some embodiments, the fluid composition 310 can comprise one or moreolefin species and one or more paraffin species. In such embodiments,capturing 320 can comprise capturing one or more olefins. In aparticular embodiment, the one or more olefin species can compriseethylene and the one or more paraffin species can comprise ethane. Inanother particular embodiment, the one or more olefin species cancomprise propylene and the one or more paraffin species can comprisepropane.

In some embodiments, the fluid composition 310 can comprise H₂S and oneor more hydrocarbon species. In such embodiments, capturing 320 cancomprise capturing H₂S. In such embodiments, capturing 320 can consistof capturing H₂S. In such embodiments, the one or more hydrocarbonspecies can comprise one or more open-chain hydrocarbons. In aparticular embodiment, the one or more open-chain hydrocarbons cancomprise propane, propene, ethane, ethene, and combinations thereof.

In some embodiments, one or more MOFs described herein are suitable forapplications involving gas, vapor, and/or solvent dehydration. Theparticular outstanding properties ofNiM_(b)F₆₋₂O_(w)(H₂O)_(x)(Ligand)_(y)(solvent)_(z), wherein M_(b) cancomprise Al, Fe, V, or Nb, for example, as compared to SIFSIX-3-M (Cu,Zn, Ni) materials, and others known in the art, in terms of stability tomoisture, and H₂O uptake and affinity make these series of novel MOFssuitable for many industrial application where various degree ofhumidity need to be removed. Furthermore, these materials areadvantageous in that exposure to moisture in non-process settings (e.g.,transport, installation, maintenance, etc.) will not affect performance.

In some embodiments, one or more MOFs described herein are suitable forapplications involving CO2 capture from flue gas, syngas, biogas andlandfill gas. In particular, MOFs, with and without open metal sites,characterized by the formula NiM_(b)F₆O_(x)(H₂O)_(y)(Ligand)_(z) exhibita number advantageous of CO₂ properties (e.g., uptake, selectivity, andkinetics) at various concentrations (e.g., from 1% to 50%) and humidityvalues (e.g., up to ca. 100% relative humidity) for a wide variety ofrelevant industrial gases.

In some embodiments, one or more MOFs described herein are suitable forapplications involving CO₂ removal in confined spaces. Efficient removalof CO₂ at low concentrations is vital for the proper operation of manyconfined-space systems, such as breathing systems. Confined spaces caninclude those found in submarines and aerospace craft. For example, inlong-term space flight and submarine missions where air resupplyopportunities are scarce, CO₂ must be removed from the air and recycled.An average crew member requires approximately 0.84 kg of oxygen andemits approximately 1 kg of carbon dioxide per day. Thus the ability tocontinuously purify exhaled air to a maximum CO₂ concentration of 2-5%will lead to an optimal recycling and considerable reduction in freshair supply in remote confined spaces. The shortcomings of existingtechnologies include a low daily capture capacity, due in part to thelong temperature swing adsorption cycling (TSA) mode, which isdetermined mainly by absorbent reactivation. In case of low CO₂concentration removal, chemical adsorbents (e.g., amine supportedabsorbents) are preferred with a heat of adsorption of 70-100 kJ/mol.The heat of adsorption indicates the energy required to clean thematerial after each adsorption cycle. The MOFs disclosed herein, such asNbOFFIVE-1-Ni, among others, operate purely on physical adsorption inprocesses such as VTSA or VSA (under mild vacuum), and therefore canboth increase the daily CO₂ removal capacity and significantly decreasethe energy needed for regeneration to lower than 2500 kJ/Kg CO₂. This issignificantly lower than the 4,000-5,000 kJ/Kg CO₂ required by liquidamine scrubbing.

In one embodiment, a representative M_(a)M_(b)F_(x)O_(y)(Ligand)₂ MOFstructure can include a Ni M_(a) constituent, a Nb M_(b) constituentgroup, and a Ligand comprising a pyrazine constituent group. FIG. 4Aillustrates powder X-ray diffraction data of NbOFFIVE-1-Ni, confirmingthe high stability of the MOF in the presence of water. FIG. 4Billustrates powder X-ray diffraction data of NbOFFIVE-1-Ni, confirmingthe high stability of the MOF in the presence of H₂S. Powder X-raydiffraction data for AlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Ni similarly showhigh stability in the presence of water and H₂S.

FIG. 5A illustrates H₂S and propane (C₃H₈) adsorption isotherms forNbOFFIVE-1-Ni. An adsorption isotherm determines the amount of adsorbedadsorbate over the dry mass of adsorbent as a function of its vaporpressure at constant temperature. The data in FIG. 5A indicates anextremely high sorption of H₂S even at low pressure and essentially zerosorption of C₃H₈, even at over 2 bar at 298K. As shown in FIG. 5A, oneor more MOFs described herein are suitable for H₂S removal from polymergrade paraffins. In particular, one or more MOFs described herein aresuitable for applications involving H₂S removal from propane. Single gasadsorption data revealed that the NbOFFIVE-1-Ni channels with restrictedaperture-size allowed the adsorption of C₃H₆ but did not permit the C₃H₈to diffuse/adsorb into the pore system at 298 K up to ca. 1 bar.Significantly, C₃H₆/C₃H₈: 50/50 mixed gas adsorption data, collected at298 K (up to 0.5 bar partial pressure of C₃H₆), overlayed perfectly withthe pure C₃H₆ adsorption isotherm and thus supported the molecularexclusion of propane from propylene. The concomitant aperture size andshape expressed in this new MOF adsorbent provided the requisitesize/shape cut-off in adsorption, resulting in the observedunprecedented infinite C₃H₆/C₃H₈ selectivity. The infinite selectivitywas further confirmed by performing C₃H₆/C₃H₈: 50/50 mixed-gas columnbreakthrough experiments, imitating the real conditions for theC₃H₆/C₃H₈ separation process, at room temperature and 1 bar in a packedcolumn bed of ca. 1.4 g of NbOFFIVE-1-Ni. Markedly, using 4 cm³/mintotal gas flow, C₃H₈ was not adsorbed in the packed column bed whilepure C₃H₆ was retained for ca. 480 seconds. Additionally, mixed-gascolumn breakthrough experiments were performed in dilute conditionsusing N₂ as a carrier inert gas, namely C₃H₆/C₃H₈/N₂: 5/5/90 andC₃H₆/C₃H₈/N₂: 25/25/90 mixtures. Noticeably, the pure C₃H₆ was retainedin the packed column bed while N₂ and C₃H₈ were not adsorbed/retained byNbOFFIVE-1-Ni. Supportively, the regeneration/activation of thesaturated adsorbent, desorption over a 10 minutes period, showed solelythe propylene signal and thus confirming the non-adsorption/retention ofthe propane in the bed

To further support and confirm the complete molecular exclusion of C₃H₈and the sole adsorption of C₃H₆, simultaneous calorimetric andgravimetric measurements (TG-DSC) were performed at 1 bar. Thiscomplementary study confirmed the complete exclusion of propane frompropylene as evidenced by the no detection of noticeable heat ofadsorption in the case of C₃H₈ and the quantified heat of adsorption forC₃H₆ of 57.4 kJ/mol. High pressure adsorption studies confirmed thenon-noticeable adsorption of C₃H₈ below 1.5 bar, only minor propaneuptake was observed at around 1.5 bar (ca. 0.1 mol/Kg).

Noticeably, the resultant infinite propylene/propane selectivity hasnever been observed using adsorbent materials. Prior C₃H₆/C₃H₈adsorption studies, using zeolite, carbon molecular sieves (CMS) orMOFs, revealed the plausible equilibrium and/or kinetic based separationbut with a low to moderate separation factors.

FIG. 5B illustrates a method for utilizing NbOFFIVE-1-Ni as a C₃H₈ sievein a two-step CSA or VSA (e.g., steps 1 and 5) as compared to the fivestep Pressure Swing Adsorption (PSA) method required by zeolites such aszeolite 4A. Valuably, the prospective deployment of NbOFFIVE-1-Ni as asplitter agent/adsorbent, permitting the complete sieving of C₃H₈ fromC₃H₆, offers: (i) a simplified separation process based on aconcentration swing recycling mode (CSRM) or a vacuum swing recyclingmode (VSRM), where the ideal working C₃H₆ capacity can be accomplishedby performing a desorption step with an inert gas (e.g. H₂ or N₂) purgeat 1.2 bar or by simply reducing the pressure from 1.2 bar to 0.01 bar,(ii) the ability to eliminate the energy-demanding high pressure stepsemployed in the case of the zeolite 4A adsorbent, that is to say nopressurization (step 2), no purge (with N₂, step 3) and no co-currentblow down (step 4) will not be required in the projected concentrationswing adsorption (CSA) or vacuum swing adsorption (VSA) system using theNbOFFIVE-1-Ni adsorbent. Markedly, the implementation of the VSA systembased on NbOFFIVE-1-Ni as an adsorbent offers potential to considerablyreduce the energy penalty associated with the conventional C₃H₆/C₃H₈separation, and valuably recover both C₃H₆ and C₃H₈ separately in a highpurity grade.

Correspondingly, subsequent mixed-gas (C₃H₆/C₃H₈: 50/50) columnbreakthrough measurements were performed in order to corroborate thepreservation of the adsorption properties and separation performance ofthe NbOFFIVE-1-Ni, namely the propylene adsorption uptake and the fullmolecular exclusion of propane from propylene at standard ambienttemperature and pressure. Distinctively, the multipleadsorption/desorption measurements (over 10 cycles) using CSRM revealedthat NbOFFIVE-1-Ni maintained its propylene adsorption capacity and itsfull molecular exclusion of propane. Detailed analysis of the data, forthe C₃H₆/C₃H₈: 50/50 mixed gas adsorption cycles in a bed comprised of1.4 g of NbOFFIVE-1-Ni, indicated a C₃H₆ uptake of ca. 0.60 mol/kg for agiven cycle based on an 8 min adsorption followed by a 10 min desorptionusing CSRM. Considerably, this result pinpoints the appropriateness ofthe NbOFFIVE-1-Ni as a stable separating agent for propylene/propanewith a pronounced propylene uptake/recovery of ca. 2 mol/Kg/hour.Markedly, the NbOFFIVE-1-Ni adsorbent offers potential to effectivelyseparate propylene from propane with a reduced energy-footprint using aconcentration swing adsorption (CSA). Perceptibly, the NbOFFIVE-1-Niadsorbent proffers a plausible large propylene recovery/productivity anda marked higher purity than to the most prominent adsorbent for the saidseparation, namely the zeolite 4A using VSA at 423 K, offering only alimited 26% recovery for a propylene capacity of 1.03 mol/Kg/hour (0.13mol/kg per cycle) with a 97% purity.

FIG. 6A illustrates ethylene and ethane sorption isotherms forNbOFFIVE-1-Ni, which show a positive correlation between increasedethane and ethylene sorption and increased pressure at 298 K. Increasedpressure increases the ethylene/ethane sorption ratio, whichdemonstrates the potential for NbOFFIVE-1-Ni in molecular sieving,particularly in olefin/paraffin separations. Similarly, FIG. 6Billustrates propylene and propene sorption isotherms for NbOFFIVE-1-Ni,which show a positive correlation between increased propylene sorptionand increased pressure and minimal propane sorption across all testpressures (0-800 Torr) at 298K. The propylene isotherms indicateBrunauer type-I adsorption characteristic of microporous adsorption atsubcritical, near critical, and supercritical conditions, which issometimes referred to as Langmuir adsorption. The plateau achieved atincreasing pressure indicates monolayer coverage or complete saturationof the adsorbant, and can imply chemisorption. It can be noted thatmonolayer coverage, or near monolayer coverage, of propylene as shown inFIG. 6B was achieved at a much lower pressure than ethylene, which, asshown in FIG. 6A, has not achieved monolayer coverage, or near monolayercoverage, even at about 800 Torr. The similarity of theadsorption/desorption curves in FIGS. 6A-B for all species (ethylene,ethane, propylene, propane) suggest that there are no MOF structuralchanges during the adsorption process.

As shown in FIGS. 6A-B, one or more MOFs described herein are suitablefor applications involving olefin/paraffin sieving separation. Inparticular, one or more MOFs described herein are suitable forapplications involving propane/propene sieving separation. For example,NbOFFIVE-1-Ni shows full sieving of propene from propane. Suchperformance is unprecedented for any class MOFs both in industry and atthe lab scale.

Similarly, one or more MOFs described herein are suitable forapplications involving BTX removal from fluid compositions comprisingH₂S. An example of a fluid composition comprising H₂S is sour gas, whichis generally defined as having more than 5.7 milligrams of H₂S per cubicmeter of gas. An example of sour gas is natural gas (CH₄) having morethan 5.7 milligrams of H₂S per cubic meter of CH₄. Removing BTX, BTEX,BTEXN, TEXS, and combinations thereof is critical to many industrialprocesses. For example, when H₂S is recovered in any industrial process,it is most commonly desulfurized by the Claus process which converts thegaseous H₂S to elemental sulfur. The Claus process includes a firstthermal combustion step which typically achieves a 60-70% conversion ofgaseous (H₂S) sulfur to elemental sulfur. A subsequent catalytic stepconverts the remaining gaseous H₂S and employs an activatedaluminum(III) and/or titanium(IV) oxide catalyst. Claus catalysts cansuffer from gradual surface area degradation in the presence ofmoisture, but are readily deactivated in the presence of BTX, BTEX,BTEXN, TEXS, and combinations thereof.

MOF's as provided herein, particularly those characterized by theformula NiM_(b)F_(6-n)(H2O/O)_(n)(pyrazine)₂(solvent)_(x), wherein M_(b)comprises Al, Fe, V, and Nb, offer an effective and unprecedentedplatform for moisture and BTX, BTEX, BTEXN, and TEXS extraction from H₂Sfluid compositions, particularly including Claus process feed streams.In particular, FIG. 7A shows benzene sorption isotherms at 293 K forNbOFFIVE-1-Ni. Benzene shows negligible adsorption, similar to thepropane adsorption shown in FIG. 6B, due in part to the large moleculesize of benzene. Similar adsorption behavior can be assumed for toluene,xylene, styrene, ethylbenzene, and naphthalene, among others. Suchnegligible adsorption is in stark comparison to that of H₂S, as shown inFIG. 6A. Therefore, NbOFFIVE-1-Ni is particularly suitable for removingH₂S from fluid compositions comprising BTX, BTEX, BTEXN, TEXS, andcombinations thereof. Such MOFs offer an attractive alternative to theactivated carbon beds currently used to remove BTX from Claus catalystprocess feed streams. This is in part because activated carbon bedsinclude a large range of microspores which allow competitive adsorptionof BTX and H₂S, and thus low H₂S/BTX selectivity. Conversely, MOFs suchas NbOFFIVE-1-Ni offer almost infinite H₂S selectivity.

FIG. 8A illustrates H₂O sorption isotherms for NbOFFIVE-1-Ni, indicatingan extremely high sorption of H₂O across all test pressures (0-1.2 Bar),and notably monolayer coverage, or near monolayer coverage, at lowpressure (e.g., 0 Bar) at 298K.

Similarly suitable for such applications are AlFFIVEH₂O-1-Ni andFeFFIVEH₂O-1-Ni. FIG. 8B illustrates variable temperature H₂O adsorptionisotherms for AlFFIVEH₂O-1-Ni, and FIG. 8C illustrates H₂O adsorptionisotherms for FeFFIVEH₂O-1-Ni at 295 K. Both adsorption isothermsexhibit unprecedented steepness at very low partial pressure thatsupports their extremely high affinity for water. Moreover,AlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Ni show exceptional adsorptionsaturation of 22 and 18 wt %, respectively, at P/P₀=0.05 relativepressure and 293 K. Heats of adsorption for AlFFIVEH₂O-1-Ni andFeFFIVEH₂O-1-Ni were determined by TG-DSC experiments to be 63 kJ/moland 64.7 kJ/mol respectively.

FIG. 8D illustrates a comparison of the relationship between wateruptake at 0.05 P/P₀, heat of sorption and regeneration temperature ofAlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Ni with other well-known dehydratingagents. It is worth mentioning that the heat of H₂O adsorption at verylow loading in case of the zeolite 5A is remarkably higher (80-120kJ/mol) than MFFIVEH₂O-1-Ni (M=Al or Fe) series and consequently thisbehavior reflects the high desorption temperature 250° C. (523K) neededto ensure optimal cyclic operations. MFFIVEH₂O-1-Ni (M=Al or Fe) havethe greatest advantage to necessitate a much less demanding energy ofH₂O vapour full desorption. In fact, activation/re-activation evaluationand adsorption/desorption cyclic properties of AlFFIVEH₂O-1-Nidemonstrated that the full dehydration is achievable after a simpleheating at 95-105° C. (368-378K) combined with flushing a lessabsorbable gas (such as N₂) or vacuum. The low temperature recyclingfeature is of prime importance as it prevents all the concerns withregards to coke formation, commonly occurring using zeolites, when thedehydration is carried out in the presence of hydrocarbon and/or VOC athigh temperatures. Silica gel can be recycled by heating only at 90-100°C. with a H₂O heat of adsorption of 43-50 kJ/mol, but it exhibits muchlower H₂O adsorption uptake at low H₂O vapor partial pressures as it isshown in FIG. 8D. Similar to the 3 A, 4 A, and 5 A molecular sieves,MFFIVEH₂O-1-Ni MOFs exhibit an excellent rate of H₂O adsorption and muchbetter adsorption kinetics than other types of desiccants.

FIG. 9A illustrates a CO₂ isotherm up to 1 bar at 298K for NbOFFIVE-1-Niand FIG. 9B illustrates a variable temperature adsorption isotherm forNbOFFIVE-1-Ni at temperatures ranging from 258K to 348K. NbOFFIVE-1-Nishows steep adsorption isotherms for CO₂. FIG. 9C illustrates lowpressure CO₂ isotherms for various MOFs, and shows that NbOFFIVE-1-Nioutperforms SIFSIX-3-Cu, the best known trace CO₂ capture MOF.NbOFFIVE-1-Ni absorbs 51.4 cm³/cm³ (1.3 mmol/g) CO₂ at 400 ppm and 298Kas compared to 44.6 cm³/cm³ by SIFSIX-3-Cu, 15% higher than the bestreported material. Consequently, NbOFFIVE-1-Ni is the best material forgravimetric and volumetric CO₂ capture at trace concentration, drivenmainly by physisorption. The difference in uptake is observed evenlarger at higher temperatures where NbOFFIVE-1-Ni absorbs 63% more CO₂at 400 ppm and 328K than SIFSIX-3-Cu. The volumetric uptake forwell-known MOFs such as Mg-MOF-74 is comparatively very small at 400 ppm(≈1.7 cm³/cm³). In terms of gravimetric uptake both NbOFFIVE-1-Ni andSIFSIX-3-Cu have similar CO₂ capacity and adsorb 43 cm³ STP/g at 1300ppm and 298K, 300% higher than SAPO-34 (Sr²⁺), a physical adsorbentcandidate for CO₂ removal in long-duration crewed space explorationmissions. Recently, a copper silicate (SGU-29) was reported showing ca.26 cm³/cm³ and 40 cm³/cm³ uptake at CO₂ concentration of 400 and 1000ppm (single gas adsorption), respectively. The CO₂ volumetric andgravimetric uptakes of this purely inorganic CO₂ adsorbent is much lowerthan NbOFFIVE-1-Ni at very low CO₂ pressure.

Fourier difference data obtained through single crystal X-raydiffraction (SCXRD) of a degassed crystal of NbOFFIVE-1-Ni under 1 barCO₂ atmosphere at 298K, indicated a clearly localized CO₂ moleculewithin the 1D channels of the structure. FIGS. 9D and 9E provide directvisualization of CO₂ molecules inside the crystal structure ofNbOFFIVE-1-Ni showing the energetically highly favorable arrangement ofCO₂ molecules inside the channels along [010] and [001], respectively.CO₂ occupies highly energetically favorable position, whereelectropositive carbon of CO₂ is surrounded by four electronegativefluorine of (NbOF₅)²⁻ groups (C . . . F distance=3.04(1) Å) andelectronegative oxygen atoms of CO₂ is surrounded by pyrazine hydrogens(C—H . . . O distance=2.98(1) Å, angle=119.9°). It can be inferred fromthe crystal structure that presence of strong complementary interactionsat right position create energetically highly favorable ‘sweet spot’ forCO₂ that is responsible for uniquely strong physiosorption-driven CO₂capture features in this material. The highly favorable interactions forCO₂ in case of NbOFFIVE-1-Ni are reflected in the value of heat of CO₂adsorption, shown in FIG. 9F, which are comparable to that ofSIFSIX-3-Cu. The heat of CO₂ adsorption for NbOFFIVE-1-Ni was determinedusing variable temperature isotherms and further confirmed by directTG-DSC measurement.

FIG. 9G illustrates cyclic CO₂ (1%)/N₂(99%) column breakthroughexperiments at 298K in both dry and humid conditions. The breakthroughtime under dry condition for 1% CO₂ in the gas stream with the flow rateof 10 cc/min was impressive 415 min/g (8.2 wt %).

Advantageously, the presence of humidity (75% RH) did not significantlyalter the CO₂ breakthrough time (283 min/g, uptake of 5.6 wt %). Inaddition, the CO₂ uptakes in dry and humid streams were reproducibleafter reactivation at 378K. Interestingly, the water vapor was retainedin the column for 1100 min/g which corresponds to an uptake of 13.8 wt%. Column breakthrough experiments were also carried out at traceconcentration of CO₂ (1000 ppm CO₂) with the flow rate of 20 cm³/min,proving that CO₂ could be retained in the column for 1880 min/g with anuptake of 7.4 wt %.

For comparison purposes, NbOFFIVE-1-Ni was evaluated against otherbenchmark materials used in real world (both chemical and physicalabsorbents) as well as other newly developed promising materials, interms of CO₂ heat of adsorption and CO₂ removal capacity during 1 day ataround 1000 ppm CO₂. For practical purposes it was assumed that allsorbent were fully recyclable, with the exception of LiOH, which is anon-recyclable sorbent. The adsorption-desorption recycling was assumedto be 60 min (24 cycles a day) and the comparison was based on the CO₂scrubbing requirement of 1 kg of CO₂/1 day/1 person in confined spaces.The results in FIG. 9H show that NbOFFIVE-1-Ni exhibits the bestcompromise between high CO₂ capacity in 1 day (24 cycles) at 1000 ppmCO₂ and optimal heat of adsorption (or energy required for regeneration)as compared to LiOH, liquid amine, amine supported solids, zeolites 5A(Ca²⁺), SAPO-34 (Sr²⁺) and the recently unveiled copper silicate(SGU-29). All the CO₂ adsorption capacities were determined atequilibrium.

The data in FIGS. 9A-G demonstrate the applicability of NbOFFIVE-1-Niand other MOFs described herein for CO₂ capture applications in confinedspaces and/or from ambient air. Moreover, new pcu-based MOFs, such asNbOFFIVE-1-Ni, using reticular chemistry are shown to be more efficientand stable than the best-known materials for CO₂ capture fromatmospheric and confined space. Further, unlike many other MOFs,NbOFFIVE-1-Ni is easy to synthesize in large quantity (g to kg) in veryeconomical manner, making it a commercially viable candidate.

AlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Ni are similarly suitable for CO₂adsorption applications, particularly for adsorbing CO₂ from naturalgas, flue gas and syngas, as these materials show selectivity for CO₂over N₂, CH₄ and H₂. The heat of adsorption of CO₂, determined fromvariable temperature adsorption isotherms for AlFFIVEH₂O-1-Ni andFeFFIVEH₂O-1-Ni, is 45 kJ/mol and 48 kJ/mol, respectively. This wasfurther confirmed by direct calorimetric measurement of CO₂ adsorptionfor the aluminum (43 kJ/mol) and iron (45.3 kJ/mol) analogues. Bycomparison with the Qst associated to H₂O adsorption, it is clear thatthe framework-CO₂ interactions (45 kJ/mol) are much weaker than theframework-H₂O interactions, which is mainly due to water coordination tothe available open metal site in the highly confined pores.

With the aim to study the dehydration performance of MFFIVEH₂O-1-Ni forCO₂ containing gas streams in general and NG in particular, breakthroughadsorption column experiments were carried out on AlFFIVEH₂O-1-Ni forsingle water vapor in the presence of N₂, CH₄ and CO₂ using the sametotal flow (23 cm³/min) and relative humidity (75% RH). Interestingly,the H₂O retention time in the column was similar (500-600 min/g withinexperimental error) independently if CH₄ and CO₂ are present or not inthe CO₂/CH₄: 1/99 mixture. Further investigation using CO₂/N₂ mixturesystems with increasing CO₂ concentration at 1, 10 and 50% showed nochanges for the water vapor retention time in the column (500-600 min/gwithin experimental error). All these results prove that the same watervapor adsorption behavior and uptake occurred independently on the CO₂composition and the type of mixtures tested (CO₂/CH₄: 1/99, CO₂/N₂:1/99, CO₂/N₂: 10/90 and CO₂/N₂: 50/50).

On the other hand, while N₂ and CH₄ did not show any noticeable uptakein both dry and humid conditions, the retention time in the column forCO₂ during moisture containing tests was only slightly different (withinexperimental error) compared to the corresponding dry tests for all themixtures studied.). Although the AlFFIVEH₂O-1-Ni framework isenergetically favorable for H₂O adsorption, these results show that CO₂is still adsorbing in the presence of moisture.

To delineate further the mechanism occurring during the simultaneous CO₂adsorption in hydrated CO₂/N₂ and CO₂/CH₄ mixtures, post in-situtemperature programed desorption (after water vapor saturation) in thecase of CO₂/N₂/H₂O mixture was carried by heating progressively at 55°C., 85° C. and 95° C. It was observed that H₂O and CO₂ still desorb fromthe column, indicative of residual adsorbed CO₂ remaining in the poresof AlFFIVEH₂O-1-Ni even at 95° C. These result show that AlFFIVEH₂O-1-Nicould potentially adsorb CO₂ and H₂O simultaneously. In addition,calorimetric measurements of hydrated CO₂/N₂: 1/99 showed similar CO₂and H₂O heat of adsorption as compared to the corresponding values forsingle H₂O vapor and CO₂. These results represent abreakthrough/unprecedented finding in material development for CO₂capture and NG upgrading in hydrated gas streams.

Because H₂O/CO₂ separation system on AlFFIVEH₂O-1-Ni is mainly beingdriven by thermodynamics (no kinetic barrier), where CO₂ and H₂O canaccess the pore system easily, we intended to find the cut-off molecularsize imposed by the access to the pores channels. In light of thetheoretically (from crystal structure) slightly large aperture size incase of MFFIVEH₂O-1-Ni as compared to the previously reportedNbOFFIVE-1-Ni suitable for C₃H₈ full sieving, we targeted to explore theadsorption of slightly bigger probe molecules such as n-C₄H₁₀,iso-C₄H₁₀, 1-propanol and iso-propanol. AlFFIVEH₂O-1-Ni showedincreasing selectivity for isobutene, n-butane, and 1-butene.FeFFIVEH₂O-1-Ni showed increasing selectivity for isobutene andn-butane. AlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Ni each showed increasingselectivity for isopropanol, 1-propanol, and ethanol. InterestinglyAlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Ni showed no adsorption for iso-butaneand iso-propanol indicative of evident efficient dehydration, via fullsieving, of gases/vapors with equal and larger sizes than iso-butane andiso-propanol.

These results demonstrate the value of the MOF embodiment characterizedby the formula Ni(Al, Fe, V, or Nb)F₅O(pyrazine)₂(solvent)_(x) as aplatform for refining a number of valuable hydrocarbon gases and fluids,including methane and propane. Further, these results suggest this MOFcan be used to refine other hydrocarbon gases and fluids, includingethane, butane, and others. The data in FIG. 6A also suggestsNbOFFIVE-1-Ni can further be used for achieving a particularized fluidmixture. For example, a fluid stream containing initial ethylene andethane amounts can be altered by varying the pressure at which the fluidcontacts the MOF. The exemplary performance and properties of the Nb⁵⁺based MOFs disclosed herein are notably achieved in spite of having noopen metal sites. These and other results can be expected in similarother embodiments, with or without open metal sites, such as MOFstructure characterized by the formula NiM_(b)F₅O(pyrazine)₂, whereinM_(b) can be one of the following Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺,V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺. These and other results can be expectedin similar other embodiments, with or without open metal sites, such asMOF structure characterized by the formula M_(a)NbF₅O(pyrazine)₂,wherein M_(a) can be one of the following cations: Cu²⁺, Zn²⁺, Co²⁺,Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺,Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺.

Example 1 Aperture Size Modification

Altering the nature, shape, and dimensions of the pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of ligands and thus dictate themaximum and/or minimum opening of the pore aperture size. This approachoffers potential to dial-in/command the passing-blocking of specificprobe molecules. The (NbOF₅)²⁻ pillaring inorganic building block ofNbOFFIVE-1-Ni utilizing a pyrazine ligand demonstrates this approach.Analysis of the NbOFFIVE-1-Ni structure (collected at 100K) revealed theplausible smallest pore window opening associated with the relativelyhindered rotation of the (NbOF₅)²⁻ pillars and the presence of hydrogenbond interactions. As a result, the hydrogen atoms of the pyrazinelinkers circumference the resultant rectangular aperture size of2.838(1) Å prohibiting the diffusion of any molecule other than water.In order to gain a better insight on the plausible rotation and tiltingof the pyrazine linker and subsequently derive a relative maximumopening of the window, providing a gate limit for the largest moleculeto pass through, the same structure was collected and analysed at roomtemperature. Noticeably, at room temperature, the pyrazine molecules areperceived to freely rotate along the N . . . N axis, while the (NbOF₅)²⁻pillars rotate along the 4-fold axis. The concurrent pyrazine andpillars (NbOF₅)²⁻ mobility afforded a maximum window aperture size of4.752(1) Å.

To further confirm the restricted pore size opening due the hinderedrotation of pyrazine ligands at low temperature, we performed adsorptionstudies on the fully evacuated NbOFFIVE-1-Ni. As anticipated,NbOFFIVE-1-Ni did not adsorb N₂ at 77K, indicating the restricted accessto N₂ at this low cryogenic temperature due to the contracted windowaperture size. On the other hand, adsorption studies performed at roomtemperature using CO₂ as the adsorbate molecule revealed thatNbOFFIVE-1-Ni is microporous with a BET surface area of 280 m²/g and apore volume of 0.095 cm³/g.

What is claimed is:
 1. A method of CO₂ removal, comprising: contacting ametal organic framework with air from a confined space; and capturingCO₂ from the air; wherein the metal organic framework comprises: apillar of the formula (M_(b)F₅(O/H₂O)), where M_(b) is selected fromperiodic groups IIIA, IIIB, IVB, VB, VIB, and VIII, and a square grid ofthe formula (M_(a)(ligand)_(x)), where M_(a) is selected from periodicgroups IB, IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, and VIII, ligand is apolyfunctional organic ligand, and x is 1 or more, wherein the pillarassociates with the square grid to form the metal organic framework. 2.The method of claim 1, further comprising, after capturing, recyclingair having a reduced concentration of CO₂ back to the confined space. 3.The method of claim 1, further comprising regenerating the metal organicframework once a CO₂ removal capacity of the metal organic framework isreached.
 4. The method of claim 3, wherein the energy requirements forthe regenerating is about 2500 kJ/kg CO₂ or less.